Looking through the forum here, but also over at ardupilot.com and the Facebook group, one can see many folks who have either complained of poor flight performance of their IRIS or had crashes due to power loss towards the end of a flight.
Taking the data from IRIS and running it through eCalc.ch, one can very quickly see that IRIS is too heavy and underpowered to fly safely at the weight of IRIS + Gimbal + Tall Legs.
Therefore my recommendation: Don't fly your IRIS with Gimbal and long legs! It's not safe and you run a very high risk of crashing it!
Flying with the short legs and GoPro but without Gimbal is OK. Although that's not what I purchased it for.
Have a look at the table below. The "Hover Throttle (Normal)" is the amount of throttle you need to give at the beginning of the flight to keep IRIS hovering. The "Hover Throttle (Low)" is the amount of throttle you need to give when the battery is down to 25% capacity. That's about when you should land. What unfortunately becomes very clear: IRIS is not suitable to be flown with that weight at any realistic air temperature or altitude. Required hover throttle is always more than 70% (making it a "very underpowered copter"; http://copter.ardupilot.com/wiki/ac_throttlemid/). But in all cases you even go beyond 80% required throttle at the end of the flight. You can't control a quadcopter anymore at that level.
If you want to reproduce these results yourself with http://www.ecalc.ch/xcoptercalc.php, here are the values used:
# of Rotors: 4
Model Weight: 1750g (incl. Drive)
Elevation: see table above
Air Temperature: see table above
Battery Cell: Custom
Cell Capacity: 3500 mAh
Resistance: 0.0052 Ohm
C-Rate: 30C cont, 40C max
Controller: max 20A
Motor Manufacturer: RCTimer A2830-12 (850)
Propeller: APC SlowFly SF
Or use this link.
What hover throttle do you require at what air temperature and field elevation? Post some logs along with air temperature of that day and field elevation.
Here are instructions on how to determine your require Hover Throttle: Fly IRIS in Stabilize, AltHold or Loiter in a stable hover for 30-60 secs. Download the logs for that flight and open it in Mission Planner via Terminal -> Log Browse. In the right-hand tree open the "CTUN" subfolder. Click the tick box for "ThrOut". Find the stable hover period of your flight (white box in example below) and read the approx value of that period (white line in example below). You will see that in the example below it is about 84%. Post your results for IRIS with Gimbal and Tall legs along with outside air temperature and your field elevation.
I think I have to agree.
I had disappointing result with the legs and gimbal. It did work, but it was sluggish and after a few minutes up it would just drift down even at full throttle.
Im going to have one more go but using the legs available at http://www.dronehoners.com/
Ive installed them now (took about 1 week to arrive to New Zealand) and they are considerably lighter (tho feel a little less sturdy as so thin). The seem to be strong perspex type material.
Ive also got 5000mah Zippys which are a bit heavier also. Will let you know how I get on once get time to test.
One more point to Chris's post. with the full payload I found out that flying the Iris and hovering are two different worlds. Lets say hover provides 5 minutes to a 10.7 failsafe.
When you start flying around and trying to film with it in alt hold or loiter it will start losing altitude very quickly when it is trying to fly horizontally. To Christain's point, very underpowered.
I also had similar results and had previously asked for a xcoptercalc mode from 3DR..(not forthcoming) the numbers dont lie..4S just makes things worse 3 min flighttimes...
thinking its time to talk to 3DR about a RMA..
as this is NOT workable and never was doesnt matter WHAT sized battery or voltage is stuffed in..
until the arms are longer(13"prop) .. the motor pockets ditched(stronger motor) and the battery compartment left behind/ external strapon lipos things WONT improve..
NO amount of modding will do anything about those numbers till these basic facts are changed.
Underpowered or Overweight?
My quad has long legs & gimbal, fpv, telemetry. But uses 3000mah 3s. I get about 12 mins flight time before the quad starts to slow descend. Admittedly, my quad is just a cheapo, and not an Iris, but it's similar. I suggest shaving weight - smaller lipo, fewer wires, less plastic body. There's a will there's a way! here's my self built quad for an idea: http://www.rcgroups.com/forums/showthread.php?t=2104315&page=6
The weight of an Iris long leg is approximately 35.2 grams (including mounting screw and nut).
35.2gr less Dronehoners leg at 21gr is 14.2gr weight saving per leg.
Changing four legs gives a net weight reduction of approximately 56.8 grams per airframe.
A possible bonus (perhaps): drag reduction.
The Dronehoners legs are a good start. But not enough. Even leaving away the legs altogether (weight reduction of 140g) you still need 78% throttle to hover at 20C/0m alt towards the end of the flight. Flying at 20C/1000m (that's not even Denver) you already need 88%.
While reducing weight is the right approach, the legs alone aren't gonna cut it.
what is needed here is a pregnant iris.. arms extended to take at least a 12"(13" preferred) prop, unconstrained motor pockets and at least a 30amp per channel 4-1 ESC and of course a lower KV motor to match the 13"(preferred) props and after all that why bother with the IRIS??
Plenty of choices for the price of a new IRIS in CF/GF nowadays ..parted out...and some interesting alternatives such as OpenPilot and paparazzi to mention 2 but not all the alternatives.
xcoptercalc is a merciless bitch and I suspect the truth lies someplace within the numbers generated,
be interesting to see what it says about the phantom vision+ if I can find numbers for same
These numbers are very surprising - 72% at best? Is the weight accurate (1750gr)? I just don't think Iris was meant to carry a gimbal at all.
When we were tuning the Easy Drone we had to go up to 36mm motors (400W), 30A ESCs, 11" props and a 4S battery to get to 50% throttle with full weight. (http://kck.st/1gekW1T) To start at 72% is a bit dangerous I agree.
Is the weight accurate (1750gr)? I just don't think Iris was meant to carry a gimbal at all.
I do. The weight of the IRIS , at least mine, is naked including stock battery, 1290g, + Tarot Gimbal + GoPro 1590g including long printed legs (13.5g/each instead of 5.5g), which is not light, but 400g/axis is nothing unusual in the scene for a quad with 500mm dia...no sports flyer though.
But the stock battery is more than disappointing: After just 15 cycles about 2400mAh capacity left ( Yes, Im running bats down till 3.3V/cell.) Except one TGY Nano, I never had such a bad battery before. I usually buy the cheapest HK stuff. I did not use mine, since I used the 5000mAh/20C Zippys adding another 130g.
I have to admit, never checked throttle at hover. Although I agree with allmost all of Christians standpoints, I never worried about this.
Except about the 3DR stock battery , I own. I don´t use it with the Gimbal IRIS anymore. Hopefully a one out of 10000...but shipping it back to 3DR doesn´t pay off.
I think the weight is fairly accurate SANS FPV-VTX, SBEC and wiring for same or alternative battery systems for same.
And my IRIS and other craft are pushing beyond that with these additions and are being stripped of same as its just NOT feasible with the weight of the stock legs and the gimbal +gopro wireing harness ad nauseam,
xcoptercalc is somewhat close to the truth about the power levels to hover and sustain flight just not enough power to be safe under manual or APM control.
When a craft is sold as RTF with gopro gimbals and legs to accomplish a specific task it should at least be able to do the task to minimum SAFE levels 50% hover etc if we are EVER to get this industry accepted by the FAA red tape specialists.
Rules are indeed advancing soon and its best the industry get used to making true not "stretched" claims about safety and flight time.
IRIS as presently engineered appears to have been designed to answer some of the issues about beginners and their mistakes:
built up motor pockets
stronger thicker arms than a DJI 450
heavy duty landing gear to protect the gimbal and cam
Unfortunately it looks like weight was a somewhat forgotten concept after the original design or the additions were NOT considered in toto and then the customer base started demanding things like gimbals for the gopro and fpv systems.
While the craft has a safe hover unloaded its SO close to the weight margin its easily overloaded and the above beginner durability features become HARD limitations to flight duration and throttle at hover.